F. Schlenker

Anomalous Charge Noise in Superconducting Qubits

  1. B. G. Christensen,
  2. C. D. Wilen,
  3. A. Opremcak,
  4. J. Nelson,
  5. F. Schlenker,
  6. C. H. Zimonick,
  7. L. Faoro,
  8. L.B. Ioffe,
  9. Y. J. Rosen,
  10. J. L. DuBois,
  11. B. L. T. Plourde,
  12. and R. McDermott
We have used Ramsey tomography to characterize charge noise in a weakly charge-sensitive superconducting qubit. We find a charge noise that scales with frequency as 1/fα over 5 decades
with α=1.93 and a magnitude Sq(1Hz)=2.9×10−4 e2/Hz. The noise exponent and magnitude of the low-frequency noise are much larger than those seen in prior work on single electron transistors, yet are consistent with reports of frequency noise in other superconducting qubits. Moreover, we observe frequent large-amplitude jumps in offset charge exceeding 0.1e; these large discrete charge jumps are incompatible with a picture of localized dipole-like two-level fluctuators. The data reveal an unexpected dependence of charge noise on device scale and suggest models involving either charge drift or fluctuating patch potentials.
arxiv pdf

Measurement of a Superconducting Qubit with a Microwave Photon Counter

  1. A. Opremcak,
  2. I. V. Pechenezhskiy,
  3. C. Howington,
  4. B. G. Christensen,
  5. M. A. Beck,
  6. E. Leonard Jr.,
  7. J. Suttle,
  8. C. Wilen,
  9. K. N. Nesterov,
  10. G. J. Ribeill,
  11. T. Thorbeck,
  12. F. Schlenker,
  13. M.G. Vavilov,
  14. B. L. T. Plourde,
  15. and R. McDermott
Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification
of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. Here we introduce an alternative approach to measurement based on a microwave photon counter. We demonstrate raw single-shot measurement fidelity of 92%. Moreover, we exploit the intrinsic damping of the counter to extract the energy released by the measurement process, allowing repeated high-fidelity quantum non-demolition measurements. Crucially, our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage. In a future system, counter-based measurement could form the basis for a scalable quantum-to-classical interface.
arxiv pdf